This invention relates to outboard motor propulsion systems for boats and more particularly to motor mounts for such systems.
In many instances it is desirable to provide for varying the height of outboard motors mounted on transoms of boats. Outboard motors typically have a cavitation plate for prevention of cavitation or slippage of the motor propeller due to passage of air as well as water through the propeller, which results in decreased efficiency of the motor. The optimum height of the motor for control of cavitation depends on various factors, in particular the speed of the motor and the load to which it is subjected. At lower speeds a lower position of the cavitation plate is more effective, while at higher speeds and particularly for racing applications a higher position is better. An ideal solution for obtaining maximum efficiency at both high and low speeds and under other variable conditions is to provide a motor mount with capability for varying the motor height as needed for operating at both high and low speeds.
Variable-height motor mounts using slidably connected brackets are disclosed in certain prior patents. U.S. Pat. No. 4,482,330, issued to Cook, employs a pair of brackets, one connected to a transom and the other connected to a motor, with the brackets being subject to relative vertical movement by action of a hydraulic cylinder. This apparatus employs bolt-and-slot assemblies wherein side edge plates of both brackets are overlapped and are held in position by bolts extending through aligned vertical plates of the bracket. Difficulty is presented in maintaining the bolts tight enough to avoid vibration, but loose enough to allow sliding. Another apparatus using a pair of brackets separately connected to a transom and an outboard motor and provided with means for vertically moving the motor bracket is disclosed in U.S. Pat. No. 5,484,311, issued to Detwiler, et al. The brackets in this device are rectangular frames with the transom bracket located entirely inside the motor bracket. Each of the brackets has a top plate and a bottom plate connected by side plates. A single cylinder is located between horizontal plates of the transom bracket, the cylinder propelling a piston rod secured to the top plate of the motor bracket. Alignment guides are provided in the form of rods extending over the entire height of the motor bracket, passing through hollow tubular members disposed between upper and lower plates of the transom bracket. Bearings are located inside the tubular members to guide the rods in a straight, vertical path. It is desired to provide a motor mount which effectively performs required vertical movement functions and which enables enhanced dimensional stability, particularly with regard to resistance to twisting forces produced by large motors.
The present invention is directed to an outboard motor mount for supporting an outboard motor on the transom of a boat in a manner such that the height of the motor in relation to the height of the transom may be readily varied, even when the motor is in operation. The mount comprises a first, forward bracket attachable to a transom and a second, rearward bracket attachable to a motor and adapted to be moved upward and downward in relation to the first bracket. Unique structure and interconnections between the two brackets are employed to obtain an improved motor mount.
Each of the two brackets has a pair of rectangular, horizontally disposed plates, one at the top of the bracket and the other at the bottom. Top and bottom plates of each bracket are fixedly connected to L-shaped vertically extending plates, preferably L-shaped corner plates located at forward corners of the first transom bracket and at rearward corners of the second bracket. The two brackets overlap one another in that the bottom horizontal plate of the top, second bracket is placed below the upper horizontal plate of the first bracket, and the upper horizontal plate of the first bracket is placed above the bottom horizontal plate of the second bracket, between the upper and lower plates of the second bracket. All four of the horizontal plates may have the same width and length with the four corners of each of the plates being in vertical alignment with one another.
The motor mount of this invention also comprises fluid actuator means in the form of a pair of hydraulic cylinders having their lower ends connected to the bottom plate of the first bracket and their upper ends connected to upper plate of the first bracket, with the cylinder passing through an aperture in the bottom horizontal plate of the second bracket and adapted for sliding vertical movement of the apertured plate along the length of the cylinders. The cylinders each contains a hydraulically actuated piston connected to a rod at the lower end of the rod, with the upper end of the rod connected to the upper horizontal plate of the second bracket. This enables the second bracket to be moved up and down upon introduction of pressurized fluid into an appropriate locations in the cylinder.
The motor mount of this invention also comprises vertically extending rods at selected locations to counteract twisting effects resulting from operation of the motor. The anti-twisting rods may extend from the bottom plate to the top plate of each bracket, with a preferred arrangement being two such rods in each bracket placed at opposite locations between the cylinders and adjacent plate edges.
The cylinders are provided in assemblies which include material and structures selected to provide a bearing effect and to maintain vertical alignment of the plates and brackets.
It is therefor an object of this invention to provide a variable height motor mount for connecting an outboard motor to a boat transom wherein a range of vertical movements may be obtained.
Another object is to provide such a motor mount having increased strength and resistance to twisting effects.
Other objects and advantages of the invention will be apparent from the following detailed description.